Generally speaking, a cardiac pacemaker or implantable pulse generator (IPG) is an electrical device used to supplant some or all of an abnormal heart's natural pacing function, by delivering appropriately timed electrical stimulation signals designed to cause the myocardium of the heart to contract or "beat".
Using telemetry, modern pacemakers are often programmable with regard to data and functionality prior to, and even after implant. Typical pacemakers are enclosed by metal casings such as titanium, which has good body compatibility. However, metal enclosures often cause interference during telemetry.
To create pacemakers and other implantable medical devices with enclosures which are transparent to radio frequency (RF) waves during telemetry, the enclosure can be constructed of ceramic material, for example. Such is the approach of U.S. Pat. No. 4,785,827 issued to Fischer, and U.S. Pat. No. 4,991,582 issued to Byers et al. Both references are hereby expressly incorporated by reference.
Implantable medical devices of the above-mentioned type have a hybrid circuit with feedthroughs attached thereto and leading through a glass-to-metal feedthrough substrate to the connector block for electrical coupling to a lead (for stimulating, sensing, or both functions). As a result of the construction of prior art substrates, fewer feedthroughs can be handled than is desirable, and costs of producing such substrates is expensive.